角钢的取样位置在腿部长度的（）。
A.1/3
B.1/4
C.1/2
参考答案：A
The two boys _____ late yesterday. [ ]
A. are all
B. are both
C. were all
D. were both
流体与固体表面之间的热量传递只是热对流的结果.
